A device for calibrating a gas meter, in which gas to be analyzed is pumped by means of a delivery device from a gas inlet to a gas outlet of a measuring chamber, has been known from DE 35 21 535. To generate a calibrating gas mixture, a defined amount of liquid calibrating substance is delivered with a metering pump from a storage tank into the measuring chamber. The calibrating substance evaporates there and mixes with a purge gas present in the measuring chamber to form a calibrating gas of a predetermined composition. The mixing of the calibrating substance is facilitated by a heater located in the measuring chamber and the convection caused by it within the measuring chamber.
The drawback of the prior-art device is that an expensive pump is needed for the accurate metering of the calibrating substance in order to set a defined percentage of the calibrating substance in the gas to be analyzed. In addition, stable temperature conditions must prevail in the measuring chamber, which cannot be ensured without difficulties in the case of portable meters, which must be small and compact.
A process for determining certain characteristics of a substance that can be caused to engage in electrochemical reactions in a gas sample was disclosed in DE 43 44 196. It was found that the sensor current curves of the electrochemical gas-measuring cell have different rates of reaction for different alcohols. Thus, the rate of reaction for methanol in the measuring cell is only one fifth that for ethanol. Identification of the substance present is possible based on the different rates of reaction.